Quantum Mechanics: Explained for a Novice

[jcsd]

Originally posted by FZ+
By Copenhagen, ghost electrons go left and right, you collapse the wavefunction of the one you measure. How this is decided is random.

By Everett, yes. But which universe "you" are in is random. ie. there is no single special you.

No, in the Copenhagen interpretation the wavefunction is a purely mathematical construct, you don't get 'ghost electrons'. In David Deutsch's variation of Everett's MWI you have 'shadow electrons' which travel both paths.

 

[steersman]

By Copenhagen, ghost electrons go left and right, you collapse the wavefunction of the one you measure. How this is decided is random.
By Everett, yes. But which universe "you" are in is random. ie. there is no single special you.

Just to clarify, is the phenomona you described the reason these particles are random/produce random effects?

If it is then we need to go back a bit,

Why were the interpretations of Copehagen and Everett needed? What are they explaining? What was wrong with the status-quo?

How do you know both electrons go left and right if the universe breaks off and only one event is observed?

 

[selfAdjoint]

Originally posted by steersman
Just to clarify, is the phenomona you described the reason these particles are random/produce random effects?

If it is then we need to go back a bit,

Why were the interpretations of Copehagen and Everett needed? What are they explaining? What was wrong with the status-quo?

How do you know both electrons go left and right if the universe breaks off and only one event is observed?

You don't. This is an interpretation. The problem is that quantum mechanics has two parts to it. The evolution part which is nice and smooth and analytical, and the "wave collapse" or "reduction" part which is as unsmooth as can be and paradoxical besides. Many physicists agonized over Collapse of the Wave Function, aka the Measurement Problem. Everett saw a way to avoid the problem by assuming that the wave function doesn't collapse to some eigenvalue, rather the world splits into enough copies to hold it with each of the possible eigenvalues. This leaves the wave function always smooth and analytic - i.e. always usable for calculations, but spread over many "branches" of the world.

 

[steersman]

selfadjoint said:

Everett saw a way to avoid the problem by assuming that the wave function doesn't collapse to some eigenvalue, rather the world splits into enough copies to hold it with each of the possible eigenvalues.

I still don't see what's wrong with collapsing to a single value. What are these interpretations explaining away?

 

[steersman]

Besides, what degree of measurement would it take to collapse the function - especially when speed and position can not be known?

 

[FabioF]

... a small addition to the discussion ...

Hi,
the main problem physicists have in front of them is NOT to explain "why" things happens, but "how" they do. In this sense, having a perfectly working, purely probabilistic theory to explain the behaviour of electrons, or whatever, should be just enough for a physicist.
Tring to find some hidden reason behind that thery or, even worst, behind its mathematical representation (which is basically the most convenient tool to expose the theory using a shared language), it's matter of philosophy, not physics.
I think this discussion'd better placed in www.phylosophyforums.com[/URL] :)
What do you think?
bye
Fabio

 

[selfAdjoint]

Like it or not, interpretation is one of the things physicists do. "Shut up and calculate" is good advice but it only works as long as you are calculating. Many physicists - and some of the best of them - concern themselves with questions of interpretation, and we can't just delegate that job to the physicsits.

What I wish is that somebody would lay out the consistent histories approach, not the dumbed down version for the public but the one with the details that impresses some of the finest minds in physics.

 

[steersman]

FabioF:

I know for a fact that the questions I'm asking can be answered by the "how" branch i.e. science. I'm not interested in interpretations so much as I'm interested in the facts that lead to problems that lead to interpretations. I'm all for sticking to the facts until I can understand them.

Just on a side note, there is no branch of thinking that can adequately deal with the "why", not even philosophy - unless you completely discount causality.